East of Huntsville, the 2,140 acre Monte Sano State Park has a 30 mile singletrack loop with limited stretchs of doubletrack & pavement. The trails are very rocky with lots of tough (at least for Alabama), but short climbs and numerous switchbacks.
To reach the mountain biking trailhead from Huntsville, head east on US431 to Monte Sano Blvd. Head north on Monte Sano Blvd. Turn right heading east on Nolen Ave. into the park.
Overall, Monte Sano State Park is the 3rd most popular mountain bike trail of all 10 mountain biking rides in Alabama.